Organizing Data in Software Engineering: Factorization Techniques and Refactoring Strategies

1. CSSE 375Organizing Data – Part 2 Shawn and Steve Continue the same quiz!

2. Mathematics: Factor fac·tor • One of two or more quantities that divides a given quantity without a remainder, for example: • 2 and 5 are factors of 10 • a and b are factors of ab • (a+1) and (a+3) are factors of a2 + 4a + 3 fac·tor·ing • To determine or indicate explicitly the factors of Reconsidering Q1…

3. Software Engineering: Factoring • fac·tor • Individual items that combined together form a complete software system: • identifiers • contents of function • contents of classes and place in inheritance hierarchy • fac·tor·ing • Determining the items, at design time, that make up or compose a software system Q9

4. Organizing Data • Refactorings that make working with data easier – Lots of them! • Self Encapsulate Field • Replace Data Value with Object • Change Value to Reference • Change Reference to Value • Replace Array with Object • Duplicate Observed Data • Change Unidirectional Association to Bidirectional • Change Bidirectional Association to Unidirectional • Replace Magic Number with Symbolic Constant • Encapsulate Field • Encapsulate Collection • Replace Record with Data Class • Replace Type Code with Class • Replace Type Code with Subclasses • Replace Type Code with State/Strategy • Replace Subclass with Fields

5. Replace Array with Object • Situation: You have an array in which certain elements mean different things • Solution: Replace the array with an object that has a field for each element • Similarly, Replace Record with Data Class String[] row = new String[3]; row [0] = "Liverpool"; row [1] = "15"; Performance row = new Performance(); row.setName("Liverpool"); row.setWins("15"); Q10

6. Duplicate Observed Data • Situation: You have domain data available only in a GUI control, and domain methods need access. • Solution: Copy the data to a domain object. Set up an observer to synchronize the two pieces of data. Q11

7. Replace Type Code with Class • Situation: A class has a numeric type code that does not affect its behavior • Solution: Replace the number with a new class Q12

8. Replace Type Code with Subclasses • Situation: You have an immutable type code that affects the behavior of a class • Solution: Replace the type code with subclasses Q13

9. Encapsulate Collection • Situation: A method returns a collection • Solution: Make it return a read-only view and provide add/remove methods Q14

10. Replace Subclass with Fields • Situation: You have subclasses that vary only in methods that return constant data • Solution: Change the methods to superclass fields and eliminate the subclasses

11. Replace Type Code with State/Strategy • Situation: You have a type code that affects the behavior of a class, but you cannot use subclassing • Solution: Replace the type code with a state object

12. Replace Type Code with State/Strategy class Employee { private int _type; static final int ENGINEER = 0; static final int SALESMAN = 1; static final int MANAGER = 2; Employee (int type) {_type = type;) } intpayAmount() { switch (_type) { case ENGINEER: return _monthlySalary; case SALESMAN: return _monthlySalary + _commission; case MANAGER: return _monthlySalary + _bonus; default: throw new Exception("Incorrect Code"); } } Q15

13. First Self Encapsulate Type code … Employee (int type) { setType (type);} intgetType() { return _type;} void setType(intarg) { _type = arg;} intpayAmount() { switch (getType()) { case ENGINEER: return _monthlySalary; case SALESMAN: return _monthlySalary + _commission; case MANAGER: return _monthlySalary + _bonus; default: throw new RuntimeException("Incorrect Employee"); } } Self-Encaps

14. Declare State Class and Subclasses… abstract class EmployeeType{ abstract intgetTypeCode(); } class Engineer extends EmployeeType{ intgetTypeCode () { return Employee.ENGINEER; } } class Manager extends EmployeeType{ intgetTypeCode () { return Employee.MANAGER; } } class Salesman extends EmployeeType{ intgetTypeCode () { return Employee.SALESMAN; } } Abstract Class Subclasses

15. Hook Subclasses into Employee… class Employee... private EmployeeType_type; intgetType() { return _type.getTypeCode(); } void setType(intarg) { switch (arg) { case ENGINEER: _type = new Engineer(); break; case SALESMAN: _type = new Salesman(); break; case MANAGER: _type = new Manager(); break; default: throw new Exception("Incorrect Code"); } } Employee Type Set via Accessors

16. Create a factory method for employee types… class Employee... void setType(intarg) { _type = EmployeeType.newType(arg); } class EmployeeType... static EmployeeTypenewType(int code) { switch (code) { case ENGINEER: return new Engineer(); case SALESMAN: return new Salesman(); case MANAGER: return new Manager(); default: throw new Exception("Incorrect Code"); } } static final int ENGINEER = 0; static final int SALESMAN = 1; static final int MANAGER = 2; Factory MethodFor Employee Type

17. Remove the type code definitions … class Employee... intpayAmount() { switch (getType()) { case EmployeeType.ENGINEER: return _monthlySalary; case EmployeeType.SALESMAN: return _monthlySalary + _commission; case EmployeeType.MANAGER: return _monthlySalary + _bonus; default: throw new Exception("Incorrect Code"); } } • Exercise: Now ready to use Replace Conditional with Polymorphism on payAmount Q16

18. Replace Conditional with Polymorphism on payAmount class Salesman... intpayAmount(Employeeemp) { return emp.getMonthlySalary() + emp.getCommission(); } class Manager... intpayAmount(Employeeemp) { return emp.getMonthlySalary() + emp.getBonus(); } … class EmployeeType... abstract intpayAmount(Employeeemp); Declare superclass method abstract Q16 - cntd